Recovery of indium



2,211,970 I orrlce aEoovEnY'o'F INDIUM Homer M. Doran, Meryl A. Jackson,and Alfred I. All, Great Falls, Mont., assignors to Anaconda CopperMining Company, New York, N. Y., a corporation of Montana I No Drawing.Application October 7, 1940,

Y Serial No. 360,128

7 Claims.

This invention relates to the treatment of indiurn-bearing solutions forthe precipitation of indium therefrom, and has for its principal objectthe provision of an improved procedure for the precipitation of indiumin metallic form from such solutions.

In processes for .the production of metallic indium from indium-bearingmaterials, it is customary to leach the indium-bearing material with anacid or otherwise treat it in order to produce an aqueous indium-bearingsolution. This solution is usually subjected to a series of treatmentsdesigned to eliminate impurities; and the resulting partially purifiedsolution is treated .with metallic zinc to precipitate the indium inmetallie form. 'The metallic indium t us produced is briquetted andmelted, usually u der a cover of fused caustic soda to preventcontamination, .and either is cast directly into pigs for the market, oris cast into anodes for further purification by electrolysis.

Although metallic zinc is an effective precipitant for indium, its usein commercial processes for the'production of indium for the market isaccompanied by a number of disadvantages. One

of these disadvantages is that the indium sponge precipitated bymetallic zinc often adheres quite closely to the zinc precipitant, andto separate the indium it must be scraped from the zinc sheet conditionsit leads to the precipitation of a very finelydivided indium spongewhich'is difllcult to briquette preparatoryto melting, or even to meltdirectly. p

The present invention provides, in a process involving treatment ofan'indium-bearing solution to precipitate indium therefrom, theimprovement which-comprises treating the solution with metallic aluminumin such manner as to cause a precipitate 'of metallic indium to be.formed. By employing metallic aluminum as the precipitant for theindium, avery spongy indium'precipitate is formed which does not adheretightly to the aluminum precipitant and which therefore can be separatedfrom the solution and from the precipitant without being contaminatedto'any appreciable extent by the aluminum. Indeed, if the aluminumprecipitant is employed under conditions most favorableto speedy andeffective indium precipitation, a sponge is Obtained which floats tothesurface of thesolution and which 'may be readily skimmed therefrom,washed, and briquetted preparatory to melting.

A further disadvantage of the I The indium-bearing solution from whichmetallic indium is to be precipitated in accordance with the inventionmay be prepared in any suitable manner. For example, anaqueousindium-bearing solution may be obtained from an indium-bearingzinc calcine or zinc oxide fume,

and may be suitably purified preparatory to pre- I cipitationof.metallic indium, in the manner described in our copendi'ngapplication Serial No.

333,920, filed May 8, 1940. However, it is,under-. v

stood that the method of the present invention is equally applicable tothe treatment of indiumdesirable if the indium-bearing solution isprepared, as is usuallyv the case in commercial practice, from azinciferous material and therefore contains some zinc in solution. Ingeneral the acidity of the indium-bearing solution preparatory totreatment with the metallic aluminum is adjusted to a valuecorresponding to about 100 to grams per liter H-S04. of the acidity ofthe solution is in most cases accomplished by adding the indicatedquantity of commercial aqueoussulphuric acid" to the 'solution.Precipitation of the metallic indium generally' proceeds most favorablywith the solution acidified approximatelylito the degree stated.

It is advantageous to activate the solution preparatory to treatmentwith themetallic 7 aluminum by adding tothe solutiong'an appreciablequantity of hydrochloric acid. Activation of the solution in this mannerhas the effect of materially increasing the speed with which the indiumis precipitatedby the aluminum. In the case of indium-bearing solutions;prepared and purified for precipitation of the-indium in accordance withthe procedure described in our above-ment oned copending applicationSerial No. 333,920, and acidified with sulphuric acid in an amountcorresponding to about to example, wire shavings, granules, or the like,

but ordinarily it is most convenient to employ relatively thin strips orsheets of metallic alumi-' hum which are suitably immersed below thesur- 4 I This adjustment face of the solution in the vessel in whichprecipitation is carried out. The aluminum displaces the indium from thesolution, the latter generally being precipitated in the form of asponge.

The solution in contact with the aluminumf surface of the solution. Thesponge may then be skimmed or otherwise separated from, the solution andmay be briquetted by squeezing into desired shapes. The briquettes,after washing with water to remove excess acid, are melted,advantageously under a fused cover of caustic soda to prevent oxidationor other contamination of the indium from the atmosphere, and cast intoshapes suitable either for the market or for further electrolyticpurification.

A few precautions should be observed in employing metallic aluminum toprecipitate indium from solutions. If the solution contains zinc, it isinadvisable to heat the solution to a temperature very much above 80 C.At such elevated temperaturesthe aluminum may cause precipitation ofsome zinc along with the indiumv and so yield a zinc-contaminatedproduct.

It is sometimes advisable to adjust the concentration of iridium in thesolution at the start of the precipitation operation to a value notexceeding about 80 grams indium per li'er. At higher'concentrations, theindium may precipitate more as a plate than as a sponge. Once an indiumplate is formed over the surface of the aluminum precipitant, thereaction slows down, and eventually will stop when the entire surface,of the aluminum precipitant is thus covered.

Thefindium plate then must be removed from the aluminum before furtherprecipitation of indium can be carried out with the same precipitant.Ordinarily this deposition of the indium as a plate on the precipitantdoes not occur during precipitation of indium from the originalindium-bearing solution.- If, however, on account of the presence ofundesirable impurities in the indium sponge at first produced, thesponge is redissolved and reprecipitated, the concentration of indium inthe solution from which the reprecipitation is carried out should becarefully controlled so as not to exceed about 80 grams per liter.

By employing aluminum in accordance with the invention, rather than zincas has heretofore been customary, to precipitate indium from solutions,the danger of debasing the indium precipitate with particles of zinc isavoided. It has been our observation that ordinarily no aluminum findsits way into the indium sponge. If it should, however, it would beeliminated upon melting the sponge under a cover of fused caustic soda,for aluminum is readily soluble in the hot caustic. cipitant results inthe production of an indium sponge having physicalcharacteristics whichmakes it much easier to briquette, wash, and melt than is the case whena zinc precipitant is employed. Even if the original indium-bearingsolution contains considerable quantities of zinc in solution, verylittle or none of this zinc is pre- The use of aluminum as the pre-'cipitated by the aluminum if theioperating precautions described aboveare observed.

We claim:

1. Ina process involving treatment of an aqueous indium-bearing solutionto precipitate indium therefrom, the step which comprises treating thesolution with metallic aluminum in such manner .as to cause asubstantially spongy precipitate of metallic indium to be formed.

2. In a process involving treatment of an aqueous indium-bearingsolution to precipitate indium therefrom, the steps which compriseadjusting the acidity of the solution to a value corresponding to about100 to 150 grams per liter H2804, and treating the solution withmetallicaliuninum' in .such manner as to cause a substantially spongyprecipitate of metallic indium to be formed.

3. In a process involving treatment of an aqueous indium-bearingsolution to precipitate indium therefrom, the steps which compriseheating the solution to a temperature of the order of about 70 to 80 C.,and treating the solution with metallic aluminum in such manner as tocause a substantially spongy precipitate of metallic aluminum to beformed.

4. In a process involving treatment of an aqueous indium-bearingsolution to precipitate indium therefrom, the steps which compriseactivating the solution by adding thereto an appreciable quantity ofhydrochloric'acid, and treating the thus-activated solution withmetallic aluminum in such manner as to cause a substantially spongyprecipitate of metallic indium to be formed.

5. In a process involving treatment of an aque ous indium-bearingsolution to precipitate indium therefrom, the steps which compriseadjusting the acidity of the solution to a value corresponding to about100 to 150 grams per liter H2304, activating the solution by addinghydrochloric acid thereto in amount corresponding to about 3% by volumecommercial concentrated aqueous hydrochloric acid, and treating theresulting activated solution with metallic aluminum in such manner as tocause a substantially spongy precipitate of metallic indium to be 1formed.

. um therefrom, the steps which comprise adjusting the concentration ofindium in the solution to a value not substantially exceeding about 80grams indium per liter, and treating such solution withmetallic-aluminum in such manner as to cause a substantially spongyprecipitate of metallic indium to be formed.

'7. The method of recovering metallic indium from an indium-bearingsolution which comprises adjusting the concentration of indium in thesolution to a value not substantially exceeding about grams indium perliter, adjusting the acidity of the solution to a value corresponding toabout to grams pe'r liter H:- "hactivating the solution by incorpora2:1;":-- 4 r an appreciable quantity of hydrochiozizacid, heating thesolution to a temperature of the order of l0-80 C., treating theresulting solution with metallic aluminum, whereby metallic spongeindium is caused to precipitate from solution, and separating the spongeindium thus produced from the solution.

Korma M. DORAN'. MERYL a JACKSON. ALFRED I. ALF.

